The wave of candidate announcements that began late last month has set off a new phase of volatile polling, when voters will rally behind news-making candidates and move on as soon as the next arrives.

Republican voters are just starting to tune in, and they start with few allegiances to this year’s deep field of candidates. As Republican hopefuls announce their bids and attract media attention, they’ll probably get a bounce in the polls. These bumps could easily be enough to give long-shot candidates the lead. But for now — and for a while — it might be wise to tune out the polls altogether.

That’s because these bounces tend to be short-lived. Mr. Cruz might already be learning this lesson. His support abruptly spiked after his March 23 announcement, but his standing has already slipped back under 10 percent in each of the last three polls. Without sustained news media attention, his numbers could slip further.

Mr. Rubio’s well-received announcement has been enough to give him a nominal lead in some recent national polls. But it’s hard to say whether he’ll have more staying power than Mr. Cruz.

Mr. Cruz and Mr. Rubio won’t be the last candidates to surge in the polls. Carly Fiorina, Mike Huckabee and Ben Carson are expected to announce presidential bids early next month. It would not be surprising if Mr. Carson and Mr. Huckabee, who hold at least as much support as Mr. Rubio or Mr. Cruz did before their announcements, managed to leap into double digits, or even to a nominal lead, by this time next month.

Jeb Bush and Scott Walker, or even Rick Perry and Chris Christie, could get their own boosts if they enter the race later this spring or summer.

Mr. Cruz and Mr. Rubio’s surges weren’t even that big, an increase of about six percentage points to perhaps 12 or 13 percent over all. These figures are impressive only in the context of a field in which no candidate consistently exceeds 15 percent of the vote, and in which a relatively modest bump from a modest starting point is enough to catapult a candidate to the top of the pack.

There’s nothing about drawing 10 to 15 percent of the vote in national polls that suggests a particularly strong primary candidate. Plenty of candidates have gone on to lose with far more support in the polls (although Bill Clinton won the nomination with single-digit support at this stage).

Some might say that Mr. Rubio and Mr. Cruz’s support is enough to put them alongside Mr. Bush or Mr. Walker, the two candidates who have led the polls and have often been described as front-runners for the nomination. But Mr. Bush and Mr. Walker are front-runners in spite of their standing in the polls, not because of it.

They’re front-runners because the other candidates do not appear to have enough support from party elites to sustain a national campaign. Those other candidates do not have natural factional bases — like moderates for Mr. Bush, and conservatives for Mr. Walker — that give them clear opportunities to win early contests, or do not have the potential to build broad enough coalitions to win the nomination.

Historically, the polling numbers for Mr. Bush and Mr. Walker are weak with respect to their odds of winning the nomination, which is as much an indictment of the rest of the field’s viability as it is a testament to their potential strength. Mr. Rubio is perhaps the only candidate with a good chance to join them at the top.

At some point, Mr. Walker, Mr. Bush and Mr. Rubio will need to take the lead in the polls, particularly in Iowa and New Hampshire. But now, it’s better to focus on the fundamentals — whether the candidates appear to hold the support from party elites necessary to win the nomination, whether they are broadly appealing throughout the party, and whether they seem capable of building support in the early states.

These factors, not their post-rollout bounces, will decide whether they can take the lead — and keep it.